Echo – Song Jia, Wang Yang

Female police officer Ran Dongdong shot and killed the hostage taker at a small supermarket on Miaoqian Street in Xijiang City. Although she received praise, Ran Dongdong was still greatly impacted by her first time shooting a real person. When she returned home, her husband Mu Dafu questioned her actions of killing the criminal, which caused Ran Dongdong to feel upset. Xijiang City experienced a homicide case where a female corpse was found by a fishing friend at the riverbank. The police began investigating the victim's identity and named the case "Da Keng Case."

After investigating the situation on the night of the Mu Dafu case, Shao Tianwei returned to the police station. Mu Dafu had gone to the hospital to visit his father and had dirtied his pants while sitting on a bench. He couldn't explain why he only returned home at 1am, which aroused suspicion from Ran Dongdong. Ran Dongdong and Mu Dafu visited Mu's parents and found out that Mu Dafu had visited his father that day because he had fallen victim to an online scam and was hospitalized. Mu Dafu borrowed 200,000 yuan from female writer Bei Zhen to resolve the matter and explained the situation to Ran Dongdong.

Thirteen years ago, Mu Dafu met Ran Dongdong through Ran Bumo's introduction. They fell in love at first sight and got along well. They even openly discussed their admiration for female student Fang Xiaoyu. In the end, Ran Dongdong asked Fang Xiaoyu to give Mu Dafu 100 flowers in exchange for him. Fang Xiaoyu did not insist, and the two happily got married. However, thirteen years later, they both feel that the other has changed. Mu Dafu feels that Ran Dongdong is no longer gentle, while Ran Dongdong feels that Mu Dafu is no longer honest.

Wu Wenchao continued to tell Ran Dongdong and Shao Tianwei about what he knew about Xia Bingqing. After receiving money from Xu Shanchuan, Xia Bingqing brought a fruit knife from home and moved into the house Xu Shanchuan rented for her. Xu Shanchuan gave Xia Bingqing an employment contract to show her parents, rationalizing her sudden wealth. Xia Bingqing accepted all of this, as well as the condition of being Xu Shanchuan's lover. Ran Dongdong still had many questions while listening to his story, and Wu Wenchao said that Xia Bingqing had not told him who the person was that raped her.

After visiting Wu Wenchao, Ran Dongdong became curious about Shen Xiaoying's attitude towards marriage as described by Wu Wenchao. After work, she went to the Lianhu Hotel for a massage and checked the schedule of the massage therapists. She continued to investigate her suspicions about Mu Dafu and found that the times he checked into a hotel did not match up with the times the massage therapist visited. When she asked Mu Dafu about it at home, he refused to say what he did during those two times. Ran Dongdong suspected that Mu Dafu was meeting with Bei Zhen during those hotel visits, but she did not have a definite answer.

Wu Wenchao planned to carry out the plan on Xu Shanchuan's birthday. Xia Bingqing was ready to jump off the building with Xu Shanchuan on that day to fake an accident. Wu Wenchao did not want to sacrifice two lives, so he gave Xia Bingqing another plan. On the night of Xu Shanchuan's birthday, Xia Bingqing invited him to celebrate and planned a big show in a five-star hotel, pretending that she had a new boyfriend and wanted to break up with Xu Shanchuan. This made Xu Shanchuan, who was already tired of Xia Bingqing, feel a little relaxed but also mixed with reluctance.

Ran Dongdong went to her parents' house to tell them that she wanted a divorce. Seeing that her parents were two people who didn't love each other but were reluctantly getting by together, she became more determined to divorce. She even found a lawyer to talk to Mu Dafu about it. Mu Dafu said that they should talk about it themselves. When discussing the divorce terms, Ran Dongdong's cold attitude hurt Mu Dafu deeply. He asked her to wait until the Da Keng Case was solved before getting a divorce. Ran Dongdong was no longer responsible for the Da Keng Case, but she continued to investigate and monitor it on her own, discussing the case with Mu Dafu.

The police team continued to search for Wu Wenchao and found his trace in the abandoned building, but they still couldn't catch him. The police found Wu Wenchao's phone signal in Zhinan City on the China-Vietnam border, but it turned out that Wu Wenchao had sent his phone to his classmate Fang Ziming in the area. After reasoning, the police believed that Wu Wenchao was probably returning to his hometown, so they prepared to investigate in Xinglong County. During the investigation, Shao Tianwei told Ran Dongdong about Mu Dafu's visit to him, and Ran Dongdong also said that she did not cut her wrists and that Mu Dafu had hallucinations.

After being detained, Wu Wenchao confessed to another part of the Da Keng Case, stating that Xu Haitao gave him 500,000 yuan to plan the disappearance of Xia Bingqing. Xu Haitao claimed that he only wanted Xia Bingqing to stop harassing Xu Shanchuan and did not ask Wu Wenchao to use violence. It was not Xu Shanchuan who instructed him to do so, but Wu Wenchao himself wanted to solve the problem out of gratitude for Xu Shanchuan buying him a house. After Xia Bingqing's death, Wu Wenchao asked Xu Haitao for the remaining payment and wanted to leave the city, but Xu Haitao claimed that he did not kill Xia Bingqing and did not know who did it.